Yes it's famously problematic. It's got better with time partly due to US based firms coming in and blanket offering lots of employees they hire there equity so

Yes it's famously problematic. It's got better with time partly due to US based firms coming in and blanket offering lots of employees they hire there equity so tax authorities were forced to figure out their policies, but for example when I joined a US FAANG from a European country in 2006 I was warned that the tax authorities might question the equity because they weren't really familiar with stock options. Mostly the issues are therefore related to strange tax rulings that would lead to bankruptcy in some cases. It's not unique to the EU, the USA also has some edge cases where people can be bankrupted by tax bills on money they never received.